1. Field of the Invention
This invention relates to a method for decorating the surface of a substrate with an embossable coating, and to the product produced by this method. More particularly, this invention relates to a method of producing an embossed coating of high pattern fidelity on a substrate, especially on a cellulosic fiber board, and to the product produced thereby; the embossment can be produced without deforming the substrate.
2. Description of the Prior Art
The practice of embossing patterns and designs on the surfaces of ceiling tiles, ceiling panels and other substrates is widespread and the art of imparting a decorative appearance to these products is greatly varied. However, one basic premise, relating to the majority of the embossed products, is the fact that they receive a mechanical impression from an embossing plate or roll which deforms the substrate itself, causing the patterns to be pressed into the surface of the substrate. Other conventional methods employed, such as cutting, abrading, or routing out a portion of the surface of the substrate, also involve deformation of the substrate.
The usual prior art methods of pattern embossing are, therefore, limited to the deformation, by pressure or other means, of the substrate. In the process, the fibers of the substrate become fragmented. Also, the binder loses its cohesiveness due to the fragmentation resulting from the pressure of the embossing plate or roll. As a result, the substrate becomes weak and vulnerable to humidity and the force of gravity. Such a substrate will have poor dimensional stability, and will sag from the ceiling if it is a ceiling panel or tile. Furthermore, where such substrate is a cellulosic fiber board, water extractable color bodies, such as lignins, will migrate more readily to the surface, causing surface discoloration and yellowing, which are particularly objectionable on white ceiling tiles and lay-in panels. Another disadvantage associated with those prior art methods involving cutting, routing, and abrading is that they produce dust, thus creating a health and explosion hazard to workers. Complicated and expensive dust collection systems are required to cope with these hazards.
Prior art methods of pattern embossing are further often characterized by a great variety of processing steps, including base coating the substrate, drying, subsequent wetting and hot roll embossing, utilizing temperatures of up to 650.degree. C. Apart from the many steps involved in these prior art methods, the use of a hot roll or plate at 650.degree. C. requires a great amount of thermal energy and is accordingly not an energy efficient processing step.
It would be highly desirable if an improved method of producing an embossed coating on a substrate could be found which yields an embossed coating having a highly detailed pattern, is relatively simple and thermally efficient, and can be carried out without substantially deforming the substrate.